It’s rare that scientific journals explicitly engage philosophical conundrums, but a paper in this week’s Science magazine begins with the question: “Why do people so often make decisions that their future selves regret?” At age 18, that skull-and-crossbones tattoo seems like an unimpeachably cool idea; at 28, it’s mortifying. You meet the man of your dreams at 25 — except that your dreams have become so different by 35 that you end up divorced.

“Even at 68, people think, Ugh, I’m not the person I was at 58, but I’m sure I’ll be this way at 78,” says one of the Science studyauthors,Daniel Gilbert, a professor of psychology at Harvard University and author of the book Stumbling on Happiness.

An obvious answer to the question is that people mature — that “change is inevitable,” as British politician Benjamin Disraeli said, that “change is constant.” But after examining the responses of more than 19,000 people gathered over four months in 2011 and 2012, the researchers— Gilbert, Jordi Quoidbach, of the National Fund for Scientific Research in Belgium, and University of Virginia psychologist Timothy Wilson — discovered that even though most people acknowledge that their lives have changed over the past decade, they don’t believe change is constant. Against all evidence, most people seem to believe that who they are now is pretty much who they will be forever.

For example, the average 33-year-old surveyed expected less change over the next decade than the average 43-year-old reported actually had occurred over the past decade. As the paper says, “People, it seems, regard the present as a watershed moment at which they have finally become the person[s] they will be for the rest of their lives.” Although personality and values do tend to become more stable with age, people generally underestimate the extent of future personality shifts. The researchers call this phenomenon “the end of history illusion.”

Proving an illusion is a giant epistemological problem, which is one reason the authors recruited so many participants for their study — although many of the thousands were recruited from a website sponsored by a French reality show, Leurs Secrets du Bonheur (The Secrets of Happiness). Analyzing the answers that the volunteers provided to questions about their favorite music, food, hobbies, as well as about choices concerning friends and vacations, Quoidbach, Gilbert, and Wilson compared people at different stages of life and came to a couple of conclusions:

1. The older you get, the less you believe you have changed or will change. This finding isn’t surprising: for years, researchers have confirmed the common-sense idea that one’s personality and preferences become more stable with age. At 80, your grandfather will likely disparage whichever political party he opposes with more ferocity than he did at 65. As the Science research explains, even young people feel their current qualities are good qualities. They find it hard to imagine their beliefs and values could significantly change — even though most of us actually change our views often as time progresses.

2. In a similar vein, people have a tendency to recognize that their personalities and preferences have changed in the past but misunderstand that personalities and preferences often change in the future. As part of the research, the researchers compared how self-reported personality traits had changed among 3,808 adults recruited not by that French TV show but by the MacArthur Foundation. The participants had completed a personality survey (as part of a larger study called MIDUS, or Midlife Development in the United States) in the mid-1990s and then again in the mid-2000s. Among other things, MIDUS measures what are called the Big Five personality traits: conscientiousness, agreeableness, emotional stability (sometimes called neuroticism), openness to experience and extroversion. (You can test your Big Five here.)

The MIDUS surveys are widely accepted for their reliability, so the scientists assumed that any difference between scores in the mid-1990s and those in the mid-2000s accurately captured changes in how much people are conscientious, agreeable, stable, open and extroverted today vs. 10 years ago. The researchers then asked the participants to estimate how much their MIDUS measures would have changed from 10 years ago and how much they will change in 10 years. Most people were pretty good at estimating the difference in average MIDUS scores over the past decade, but they dramatically underestimated how much MIDUS scores change for most people in the future. In short, people may commit errors of prediction more often than they succumb to errors of memory.

As further insurance that the effect they were tracking was real, the researchers conducted another study with a smaller group of volunteers. In the original experiment, the researchers assigned the participants to either make predictions of how much they would change in the future or how much they had changed in the past — but not both — so the scientists couldn’t be sure that different people were interpreting the personality criteria in the same way. They focused on 613 adults who provided answers about both future change and past change, and the discrepancy between predictive and past change remained. Most of them predicted that they would change less over the next decade than the majority of people who reported they had actually changed. Their predictions fell short, however. In other words, people who thought they “loved” and would always prefer Rice Chex to Corn Chex became less adamant by their 50s. By their late 60s, they seemed not to care so much, which may owe partly to declining mental acuity, but may also reflect a real change in the strength and intensity of personality and preferences.

The paper shows other data: older people are less willing to pay for the same concerts and meals than younger people anticipate they would, and they are less likely to remember the name of their best friend. But that could be because older people are simply bored by familiar pleasures and have worse memories.

Whether people change — can change, do change, actually change — is surely one of the most important questions in psychobiology. The Science paper advances our understanding of the answer incrementally: we understand that we have changed, but we are uncomfortable with the idea that we will change any further. The need to change implies another question: Do we need to correct a flaw? It’s not likely that any amount of science can answer that question.